This invention relates to a novel coating composition, of controlled rheology, of a polyurethane polymer of polyisocyanate and a polymer having pendent hydroxyl containing ester groups and a rheology control agent.
Polyurethane compositions are known in the art and have been used as coating compositions, adhesives, molded into articles by conventional techniques and made into foamed products. Typical polyurethanes of a hydroxyl containing polymer and a polyisocyanate are shown in O'Brien U.S. Pat. No. 3,028,367, issued Apr. 3, 1962; Horvath U.S. Pat. No. 3,284,415, issued Nov. 8, 1966, Mayer et al. U.S. Pat. No. 3,245,941, issued Apr. 12, 1966 and British Pat. No. 1,100,386, published Jan. 24, 1968. These prior art compositions form useful products but are not economical, rapid cure compositions which give a coating with excellent appearance and adhesion to substrates, toughness and flexibility as is required by industry for coatings on trucks, airplanes, railway equipment and the like. A coating composition, described in Vasta, U.S. Pat. No. 3,558,564, issued Jan. 26, 1971, has these excellent properties which are provided by the combination of a unique hydroxy containing polymer and an organic polyisocyanate but is difficult to apply in thick films directly over prevalent zinc rich primers without surface imperfections.
The coating composition of this invention overcomes this problem by virtue of its controlled rheology and provides coatings for exterior and interior surfaces that are exposed to corrosive environments and to severe weather.